Combi, system or regular boiler: which suits your home?
Choose a boiler type around hot water demand, the existing system, available space and measured water performance.
Combi boilers
A combi normally heats domestic hot water as it is drawn, without a separate hot water cylinder. This saves cylinder space. Its available hot water flow depends on the boiler and incoming mains supply; simultaneous outlets can exceed its capacity. A larger nominal output does not fix every water-supply limitation.
System boilers
A system boiler works with a separate hot water cylinder. Stored hot water can help meet demand from several outlets, but storage volume, recovery, controls and the incoming supply all matter. Do not assume that a cylinder guarantees strong pressure or unlimited simultaneous showers. The actual installation determines whether loft storage is needed.
Regular or heat-only boilers
Regular boilers also work with a hot water cylinder. Many existing systems have feed tanks in the loft, although system arrangements vary. Keeping an appropriate existing arrangement may reduce conversion work; the engineer should assess its condition and suitability rather than recommend a change from a label alone.
What to tell the engineer
- How many baths and showers you use, and which outlets may run at the same time.
- The existing boiler, cylinder, tanks and heating controls, if known.
- Space available for equipment and any proposed changes to the property.
- Any current low-flow, pressure or heating problems.
- Future plans that may affect the heating system.
Avoid choosing on a rule of thumb alone
Bathroom and radiator counts are useful starting information. A suitable recommendation also considers heat demand, measured mains flow and pressure, hot water usage, pipework and installation requirements. If you are unsure about your existing boiler type, choose the closest option on the enquiry form and explain that it needs checking.